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.\" Copyright (c) 1980, 1991 Regents of the University of California.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" the American National Standards Committee X3, on Information
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.\" Processing Systems.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)setbuf.3 6.10 (Berkeley) 6/29/91
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.\"
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.\" Converted for Linux, Mon Nov 29 14:55:24 1993, faith@cs.unc.edu
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.\" Added section to BUGS, Sun Mar 12 22:28:33 MET 1995,
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.\" Thomas.Koenig@ciw.uni-karlsruhe.de
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.\" Correction, Sun, 11 Apr 1999 15:55:18,
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.\" Martin Vicente <martin@netadmin.dgac.fr>
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.\" Correction, 2000-03-03, Andreas Jaeger <aj@suse.de>
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.\" Added return value for setvbuf, aeb,
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.\"
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.TH SETBUF 3 2001-06-09 "Linux" "Linux Programmer's Manual"
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.SH NAME
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setbuf, setbuffer, setlinebuf, setvbuf \- stream buffering operations
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.SH SYNOPSIS
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.na
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.B #include <stdio.h>
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.sp
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.BI "void setbuf(FILE *" stream ", char *" buf );
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.br
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.BI "void setbuffer(FILE *" stream ", char *" buf ", size_t " size );
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.br
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.BI "void setlinebuf(FILE *" stream );
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.br
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.BI "int setvbuf(FILE *" stream ", char *" buf ", int " mode
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.BI ", size_t " size );
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.ad
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.SH DESCRIPTION
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The three types of buffering available are unbuffered, block buffered, and
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line buffered. When an output stream is unbuffered, information appears on
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the destination file or terminal as soon as written; when it is block
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buffered many characters are saved up and written as a block; when it is
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line buffered characters are saved up until a newline is output or input is
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read from any stream attached to a terminal device (typically stdin). The
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function
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.BR fflush (3)
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may be used to force the block out early.
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(See
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.BR fclose (3).)
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Normally all files are block buffered. When the first I/O operation occurs
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on a file,
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.BR malloc (3)
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is called, and a buffer is obtained. If a stream refers to a terminal (as
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.I stdout
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normally does) it is line buffered. The standard error stream
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.I stderr
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is always unbuffered by default.
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.PP
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The
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.BR setvbuf ()
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function may be used on any open stream to change its buffer.
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The
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.I mode
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parameter must be one of the following three macros:
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.RS
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.TP
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.B _IONBF
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unbuffered
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.TP
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.B _IOLBF
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line buffered
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.TP
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.B _IOFBF
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fully buffered
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.RE
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.PP
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Except for unbuffered files, the
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.I buf
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argument should point to a buffer at least
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.I size
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bytes long; this buffer will be used instead of the current buffer. If the
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argument
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.I buf
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is NULL,
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only the mode is affected; a new buffer will be allocated on the next read
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or write operation. The
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.BR setvbuf ()
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function may only be used after opening a stream and before any other
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operations have been performed on it.
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.PP
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The other three calls are, in effect, simply aliases for calls to
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.BR setvbuf ().
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The
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.BR setbuf ()
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function is exactly equivalent to the call
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.PP
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.RS
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setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);
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.RE
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.PP
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The
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.BR setbuffer ()
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function is the same, except that the size of the buffer is up to the
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caller, rather than being determined by the default
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.BR BUFSIZ .
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The
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.BR setlinebuf ()
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function is exactly equivalent to the call:
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.PP
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.RS
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setvbuf(stream, (char *)NULL, _IOLBF, 0);
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.RE
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.SH "RETURN VALUE"
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The function
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.BR setvbuf ()
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returns 0 on success.
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It can return any value on failure, but returns non-zero when
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.I mode
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is invalid or the request cannot be honoured. It may set
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.I errno
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on failure.
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The other functions are void.
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.SH "CONFORMING TO"
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The
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.BR setbuf ()
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and
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.BR setvbuf ()
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functions conform to C89 and C99.
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.SH BUGS
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The
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.BR setbuffer ()
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and
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.BR setlinebuf ()
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functions are not portable to versions of BSD before 4.2BSD, and
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are available under Linux since libc 4.5.21. On 4.2BSD and 4.3BSD systems,
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.BR setbuf ()
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always uses a suboptimal buffer size and should be avoided.
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.P
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You must make sure that both
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.I buf
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and the space it points to still exist by the time
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.I stream
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is closed, which also happens at program termination.
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.P
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For example, the following is illegal:
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.nf
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.sp
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#include <stdio.h>
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int main()
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{
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char buf[BUFSIZ];
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setbuf(stdin, buf);
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printf("Hello, world!\\n");
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return 0;
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}
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.fi
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.sp
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.SH "SEE ALSO"
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.BR fclose (3),
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.BR fflush (3),
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.BR fopen (3),
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.BR fread (3),
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.BR malloc (3),
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.BR printf (3),
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.BR puts (3)
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